Fix broken Change Columns button in main toolbar

I'm pretty sure this was broken during the implemenation of the sticky masthead which invalidated the selector. This should be more stable going forward in that it uses just the data-toggle without a class prefix in the selector just like the export button.
Remove nested div in serrano warning

Previously, dismissing the dialog left a big block of empty space where the alert was. This way, dismissing the dialog hides the block completely leaving now empty space.
Drop the minimum Serrano version to >= 2.0.24
Drop the minimum Serrano version to >= 2.0.18
Use logical version comparison

The previous version comparison would evaluate a version of 2.1.0 as out of date given a minimum of 2.0.18 because the for loop would return false on the micro version. The micro version should only be compared when the major and minor are equal. I expanded this out for clarity. It could be in a loop but it's not worth the possible confusion to loop over 3 elements.